Sex comparisons of non-local muscle fatigue in human elbow flexors and knee extensors

OBJECTIVES: To examine non-local muscle fatigue (NLMF) in both contralateral homologous and non-related heterogonous muscles for both sexes. METHODS: Ten men and nine women participated in this study. After the familiarization visit, subjects completed four separate randomly sequenced experimental visits, during which the fatiguing interventions (six sets of 30-second maximal isometric contractions) were performed on either their right elbow flexors or knee extensors. Before (Pre-) and after (Post-) the fatiguing interventions, the isometric strength and the corresponding surface electromyographic (EMG) amplitude were measured for the non-exercised left elbow flexors or knee extensors. RESULTS: For the non-exercised elbow flexors, the isometric strength decreased for both sexes (sex combined mean±SE: Pre vs. Post=339.67±18.02 N vs. 314.41±16.37 N; p<0.001). For the non-exercised knee extensors, there is a time ´ sex interaction (p=0.025), showing a decreased isometric knee extension strength for men (Pre vs. Post =845.02±66.26 N vs. 817.39±67.64 N; p=0.019), but not for women. CONCLUSIONS: The presence of NMLF can be affected by factors such as sex and muscle being tested. Women are less likely to demonstrate NLMF in lower body muscle groups.